Dresden 2017 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 13: Superconductivity: Fe-based Superconductors - 122

TT 13.6: Talk

Monday, March 20, 2017, 16:15–16:30, HSZ 103

Spin space anisotropy in Co-underdoped BaFe₂As₂ — •Florian Waßer¹, Chul-Ho Lee², Kunihiro Kihou², Karin Schmalzl³, Paul Steffens⁴, Navid Qureshi^1,4, and Markus Braden¹ — ¹II. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, D-50937 Köln, Germany — ²National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568, Japan — ³Jülich Centre of Neutron Scattering (JCNS), Forschungszentrum Jülich GmbH, Outstation at Institut Laue-Langevin, 71 avenue des Martyrs, 38000 Grenoble, France — ⁴Institut Laue-Langevin, 71 avenue des Martyrs, 38000 Grenoble, France

We studied by polarised inelastic neutron scattering the spin space anisotropy in Co-underdoped BaFe₂As₂ in the normal as well as in the superconducting state. The spin space anisotropy in the normal state is reminiscent of the magnetic response in the pure antiferromagnetic host compound, and displays broadened spin gaps in all three directions. In particular, the longitudinal spin excitations are largely gapped by ∼ 16 meV, which seems to be sufficient larger than twice the superconducting gap value and thus prohibits any interplay with superconductivity. Consequently, in the superconducting state, we observe an anisotropic spin resonance mode, which peaks at two different energies in the two transversal spin directions respectively. The suppression of longitudinal spin fluctuations can explain the reduced superconducting transition temperature and indicates that the coexistence of antiferromagnetic order and superconductivity occurs locally.